On 03/07/18 23:23 +0100, Jonathan Wakely wrote:
On 03/07/18 23:40 +0200, Jakub Jelinek wrote:
On Tue, Jul 03, 2018 at 10:02:47PM +0100, Jonathan Wakely wrote:
+#ifndef _GLIBCXX_BIT
+#define _GLIBCXX_BIT 1
+
+#pragma GCC system_header
+
+#if __cplusplus >= 201402L
+
+#include <type_traits>
+#include <limits>
+
+namespace std _GLIBCXX_VISIBILITY(default)
+{
+_GLIBCXX_BEGIN_NAMESPACE_VERSION
+
+ template<typename _Tp>
+ constexpr _Tp
+ __rotl(_Tp __x, unsigned int __s) noexcept
+ {
+ constexpr auto _Nd = numeric_limits<_Tp>::digits;
+ const unsigned __sN = __s % _Nd;
+ if (__sN)
+ return (__x << __sN) | (__x >> (_Nd - __sN));
Wouldn't it be better to use some branchless pattern that
GCC can also optimize well, like:
return (__x << __sN) | (__x >> ((-_sN) & (_Nd - 1)));
(iff _Nd is always power of two),
_Nd is 20 for one of the INT_N types on msp340, but we could have a
special case for the rare integer types with unusual sizes.
or perhaps
return (__x << __sN) | (__x >> ((-_sN) % _Nd));
which is going to be folded into the above one for power of two constants?
That looks good.
Committed as attached (with a test I forgot to add for popcount).
commit 796e90be02c691bc57c89172940aa047caa199ab
Author: Jonathan Wakely <jwak...@redhat.com>
Date: Wed Jul 4 00:07:43 2018 +0100
Optimize std::rotl and std::rotr, add test for std::popcount
* include/std/bit (__rotl, __rotr): Avoid branch.
(_If_is_unsigned_integer): Use remove_cv_t.
* testsuite/26_numerics/bit/bitops.count/popcount.cc: New.
diff --git a/libstdc++-v3/include/std/bit b/libstdc++-v3/include/std/bit
index 76aa0957b56..ace88954030 100644
--- a/libstdc++-v3/include/std/bit
+++ b/libstdc++-v3/include/std/bit
@@ -46,9 +46,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{
constexpr auto _Nd = numeric_limits<_Tp>::digits;
const unsigned __sN = __s % _Nd;
- if (__sN)
- return (__x << __sN) | (__x >> (_Nd - __sN));
- return __x;
+ return (__x << __sN) | (__x >> ((-__sN) % _Nd));
}
template<typename _Tp>
@@ -57,9 +55,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{
constexpr auto _Nd = numeric_limits<_Tp>::digits;
const unsigned __sN = __s % _Nd;
- if (__sN)
- return (__x >> __sN) | (__x << (_Nd - __sN));
- return __x;
+ return (__x >> __sN) | (__x << ((-__sN) % _Nd));
}
template<typename _Tp>
@@ -237,7 +233,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
template<typename _Tp, typename _Up = _Tp>
using _If_is_unsigned_integer
- = typename _If_is_unsigned_integer_type<_Tp, _Up>::type;
+ = typename _If_is_unsigned_integer_type<remove_cv_t<_Tp>, _Up>::type;
#if ! __STRICT_ANSI__
// [bitops.rot], rotating
diff --git a/libstdc++-v3/testsuite/26_numerics/bit/bitops.count/popcount.cc b/libstdc++-v3/testsuite/26_numerics/bit/bitops.count/popcount.cc
new file mode 100644
index 00000000000..2982cb19bbe
--- /dev/null
+++ b/libstdc++-v3/testsuite/26_numerics/bit/bitops.count/popcount.cc
@@ -0,0 +1,108 @@
+// Copyright (C) 2018 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library. This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3. If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-do run { target c++11 } }
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do compile { target c++2a } }
+
+#include <bit>
+
+template<typename UInt>
+constexpr auto
+test(UInt x)
+-> decltype(std::popcount(x))
+{
+ static_assert( noexcept(std::popcount(x)) );
+
+ constexpr unsigned digits = std::numeric_limits<UInt>::digits;
+
+ static_assert( std::popcount((UInt)0) == 0 );
+ static_assert( std::popcount((UInt)-1) == digits );
+ static_assert( std::popcount((UInt)-2) == digits - 1 );
+ static_assert( std::popcount((UInt)127) == 7 );
+
+ static_assert( std::popcount((UInt)1) == 1 );
+ static_assert( std::popcount((UInt)2) == 1 );
+ static_assert( std::popcount((UInt)0x70) == 3 );
+
+ if constexpr (std::numeric_limits<UInt>::digits > 8)
+ {
+ static_assert( std::popcount((UInt)(0x101)) == 2 );
+ static_assert( std::popcount((UInt)(0xfff)) == 12 );
+ }
+
+ if constexpr (std::numeric_limits<UInt>::digits > 64)
+ {
+ static_assert( std::popcount((UInt)0xffffffffffffffff) == 64 );
+ static_assert( std::popcount(0x5555555555555555 | ((UInt)1 << 64)) == 33 );
+ static_assert( std::popcount(0x5555555555555555 | ((UInt)3 << 64)) == 34 );
+ }
+
+ return true;
+}
+
+static_assert( test( (unsigned char)0 ) );
+static_assert( test( (unsigned short)0 ) );
+static_assert( test( (unsigned int)0 ) );
+static_assert( test( (unsigned long)0 ) );
+static_assert( test( (unsigned long long)0 ) );
+
+// std::popcount(T) shall not participate in overload resolution
+// unless T is an unsigned integer type.
+struct X { constexpr bool did_not_match() { return true; } };
+constexpr X test(...) { return X{}; }
+static_assert( test( (bool)0 ).did_not_match() );
+static_assert( test( (char)0 ).did_not_match() );
+static_assert( test( (int)0 ).did_not_match() );
+static_assert( test( (char16_t)0 ).did_not_match() );
+static_assert( test( (float)0 ).did_not_match() );
+static_assert( test( (void*)0 ).did_not_match() );
+static_assert( test( X{} ).did_not_match() );
+enum E : unsigned { e };
+static_assert( test( e ).did_not_match() );
+
+#ifndef __STRICT_ANSI__
+#include <cstddef>
+static_assert( std::popcount(std::byte{0x00}) == 0 );
+static_assert( std::popcount(std::byte{0x01}) == 1 );
+static_assert( std::popcount(std::byte{0x02}) == 1 );
+static_assert( std::popcount(std::byte{0x03}) == 2 );
+static_assert( std::popcount(std::byte{0x30}) == 2 );
+static_assert( std::popcount(std::byte{0x40}) == 1 );
+static_assert( std::popcount(std::byte{0x41}) == 2 );
+static_assert( std::popcount(std::byte{0xff}) == 8 );
+#else
+static_assert( test( (std::byte)0 ).did_not_match() );
+#endif
+
+#if !defined(__STRICT_ANSI__) && defined _GLIBCXX_USE_INT128
+static_assert( test( (unsigned __int128)0 ) );
+static_assert( test( (__int128)0 ).did_not_match() );
+#endif
+#if defined(__GLIBCXX_TYPE_INT_N_0)
+static_assert( test( (unsigned __GLIBCXX_TYPE_INT_N_0)0 ) );
+static_assert( test( (__GLIBCXX_TYPE_INT_N_0)0 ).did_not_match() );
+#endif
+#if defined(__GLIBCXX_TYPE_INT_N_1)
+static_assert( test( (unsigned __GLIBCXX_TYPE_INT_N_1)0 ) );
+static_assert( test( (__GLIBCXX_TYPE_INT_N_1)0 ).did_not_match() );
+#endif
+#if defined(__GLIBCXX_TYPE_INT_N_2)
+static_assert( test( (unsigned __GLIBCXX_TYPE_INT_N_2)0 ) );
+static_assert( test( (__GLIBCXX_TYPE_INT_N_2)0 ).did_not_match() );
+#endif
